The present invention relates to a method and apparatus for diagnosing overheating of a gas-cooling type electric machine and, more particularly, to an overheat diagnosing method and apparatus which enables a locating of an overheated coil or core in a gas-cooled type turbine generator by measuring a density of particles and analyzing the composition decomposed from varnish or resin insulation coated on the coil or core.
With the increasing capacity of electric machines such as, for example, turbine generators, there is an increased likelihood of an occurrence of a shortcircuit resulting from poor insulation in the generator thereby causing an unexpectedly great disaster. There is especially the high probability of the coil and core of the generator being damaged by heat. To prevent damages of electric machines such as turbine generators, an overheat diagnosing apparatus has been proposed in which an overheating of the coil or core of the electric machine is detected by measuring a density of particles decomposed from the insulating material, which insulating material is formed as a varnish or resin coated on the coil or core.
The operating principle of the above noted proposed overheating diagnosing apparatus is based on the fact that insulating material coated on the coil or core, when overheated, decomposes into small particles of the size of 0.001-1 micron. The particles spread or are suspended in the cooling gas used for cooling the coil or core which, in large turbine generators, is usually hydrogen. For the purpose of detecting an occurrence of overheating, a portion of the cooling gas is extracted from an interior of the turbine generator to enable a measurement of the density of the particles contained therein.
U.S. Pat. No. 3,427,880 provides an example of an overheat diagnosing apparatus of the aforementioned type wherein, an extracted gas is ionized and the negatively charged ions are detected as a current flowing in lead wire. However, a disadvantage of this proposed apparatus resides in the fact that the gas is extracted only from one end portion of the interior of the turbine generator and the extracted gas is detected to determine whether or not the gas includes particles. Consequently, an overheating at the other end portion of the interior of the generator is extremely difficult to detect. Moreover, even if an overheating is recognized or detected, with this proposed apparatus, it is impossible to determine the exact position of the overheating of the coil or core. Furthermore, if the detector of this proposed apparatus generates a fault signal due to a malfunctioning or unsatisfactory operation of the detector, the generator should be stopped although since it is the detector which is malfunctioning, such stoppage would naturally be unnecessary. Consequently, it is extremely desireable to provide a checking means for the detector so as to prevent the occurrence of unnecessary stoppages of the turbine generator.
The aim underlying the present invention essentially resides in providing an overheating method and diagnosing apparatus which enables a diagnosing of an exact overheating position on the coil or core in a gas-cooled type electric machine.
In accordance with advantageous features of the present invention, an overheat diagnosing apparatus is provided which includes means for selectively extracting a cooling gas from any one of a number of regions in an interior space of the electric machine, with means for detecting the density of the particles in the selectively extracted cooling gas whereby an overheat region of the machine is determined when the density of the particles in the region is higher than a predetermined level. Additionally, means are provided for analyzing the composition of the cooling gas from the selected overheat region whereby an overheat position in the selected overheat region is determined.
By virtue of the noted features of the present invention, the diagnosis of overheating is performed in two steps with the first step being that of detecting for selecting an overheating region including an overheating position and the second step being an analysis for finding out an exact overheating position by analyzing the compositions of the cooling gas.
In accordance with further features of the present invention, checking means are provided for enabling a checking of the detector of the diagnosing apparatus, with the checking means being capable of functioning or operating during the operation of the electric machine so that a stopping of the electric machines becomes totally unnecessary.
Advantageously, in accordance with the present invention, means are provided for controlling the extracting means, detecting means, and analyzing means so that the cooling gas in the selected overheat region is introduced into the analyzing means.
Preferably, the analyzing means in in the form of a gas chromatograph which is adapted to analyze the proportions of hydrocarbons contained in the cooling gas.
To facilitate the continuous monitoring of the overheat diagnosing apparatus and the electric machine, means are provided which display the results obtained in the detecting means and the analyzing means. Advantageously, a drain trap is provided for trapping water drops present in the extracted cooling gas which water droplets are condensed as the cooling gas is cooled to an ambient of room temperature.
Additionally, in order to verify the validity of the selection of the overheat region by the detecting means, in accordance with further features of the present invention, means are provided for checking the validity of such selection. Preferably, the checking means comprises a standard particle generator and a gas cylinder for supplying a carrier gas to carry the standard particles to the detecting means.
In accordance with advantageous features of the method of diagnosing overheating in a gas-cooled type electric machine, an interior space of the electric machine is divided into a plurality of regions, with a cooling gas being selectively extracted from any one of the regions. The density of the particles of organic insulating material in the extracted gas is then detected so that an overheat region including an overheat position is selected when the density of the particles in the region is higher than a predetermined level. The composition in the cooling gas from the selected overheat region is analyzed so that an overheat position in the selected overheat region is determined.
Advantageously, water drops in the extracted cooling gas are trapped and a validity of the selection of the overheat region is checked.
Accordingly, it is an object of the present invention to provide a method and apparatus for diagnosing overheating of a gas-cooled type electric machine which avoids, by simple means, shortcomings and disadvantages encountered in the prior art.
Another object of the present invention resides in providing an apparatus and method for diagnosing overheating of a gas-cooled type electric machine which considerably increases a reliability of a detector arrangement by providing a checking means for the detector.
Yet another object of the present invention resides in providing a method and apparatus for diagnosing overheating of a gas-cooled type electric machine by which it is possible to determine which regions in an interior space of the machine are overheated and to determine an exact position of the region being overheated by using a particle detector and a means for analyzing compositions contained in the gas.
A further object of the present invention resides in providing a method and apparatus for diagnosing overheating of gas-cooled type electric machines by which it is possible to confirm a validity of an overheat signal by checking detectors of the apparatus.
A still further object of the present invention resides in providing a method and apparatus for diagnosing overheating of a gas-cooled type electric machine which ensures a highly reliable diagnosis of the overheating.
Yet another object of the present invention resides in providing a method and apparatus for diagnosing overheating of a gas-cooled type electric machine by which it is possible to minimize damage to the electric machine caused by an overheating, to minimize the time necessary for repairing the machine, and to limit any adverse effect of overheating on the entire system of the plant.
A further object of the present invention resides in providing a method and apparatus for diagnosing overheating of a turbine generator which minimizes the number of times the generator has to be stopped to determine the presence of an overheating.
These and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purposes of illustration only, one embodiment in accordance with the present invention .